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KMP字符串模式匹配详解
Converting Strings To/From Ints:
atoi, itoa, sprintf and sscanf
Prev: Copying, Finding the Length of
Strings and the Null Character
Next: Copying Strings:
strcpy, strncpy and strcmp
Warning
We are leaving the basic stage for a while to talk about various useful string functions.
If you want, you can skip to abstract data types section and return here later.
Converting a String Into an int Using atoi
Before I leave the string section, I'd like to talk about two useful functions that could come in handy later on. Both of these require the stdlib.h header file.
First of all, atoi. This converts strings, like "23" or even "29dhjds" into integers (returning 23 and 29 respectively in this case).
atoi requires one char * argument and returns an int (not a float!).
If the string is empty, or first character isn't a number or a minus sign, then atoi returns 0.
If atoi encounters a non-number character, it returns the number formed up until that point.
#include <stdio.h> #include <stdlib.h> int main() { char str1[] = "124z3yu87"; char str2[] = "-3.4"; char *str3 = "e24"; printf("str1: %d\n", atoi(str1)); printf("str2: %d\n", atoi(str2)); printf("str3: %d\n", atoi(str3)); return 0; }
Output:
str1: 124
str2: -3
str3: 0
Converting an int Into a String Using itoa (NOT ANSI C)
Before I continue, I must warn you that itoa is NOT an ANSI function, (it's not a standard C function). You should use sprintf to convert an int into a string, which I'll show you in a moment.
I'll cover itoa in case you've ever wondered what it does.
itoa takes three arguments.
The first one is the integer to be converted.
The second is a char * variable - this is where the string is going to be stored. My program crashed if I pass in a char * variable I've already used, so I passed in a normal sized char array and it worked fine.
The last one is NOT the size of the array, but it's the BASE of your number - base 10 is the one you're most likely to use. Base 2 is binary, 8 is octal and 16 is hexadecimal.
For a small lesson on bases, go back to the Hexadecimal section.
itoa is a very useful function, which is supported by some compilers - shame it isn't support by all, unlike atoi.
Maybe converting a base 10 number into binary format as a string isn't so hard after all...
#include <stdio.h> #include <stdlib.h> int main() { char str[10]; /* MUST be big enough to hold all the characters of your number!! */ printf("15 in binary is %s\n", itoa(15, str, 2)); printf("15 in octal is %s\n", itoa(15, str, 8)); printf("15 in decimal is %s\n", itoa(15, str, 10)); printf("15 in hex is %s\n", itoa(15, str, 16)); return 0; }
Output:
15 in binary is 1111 |
... itoa can be useful when you know your program doesn't have to be ANSI C only.
sprintf
You can use this function as an alternative to itoa. It's only half as good as itoa because you can't specify the base of your number to be converted.
sprintf takes three arguments.
The first has to be a char * variable, which means you can use a char array, but make sure it's big enough to hold the converted number.
The second argument is a string containing a format specifier, depending on the format of the number you want to convert.
The third argument is the number you want to convert into a string.
sprintf returns the number of characters in the string (not included the null character).
This example convert a few numbers into string format, and prints out the result:
#include <stdio.h> int main() { char str[10]; /* MUST be big enough to hold all the characters of your number!! */ int i; i = sprintf(str, "%o", 15); printf("15 in octal is %s\n", str); printf("sprintf returns: %d\n\n", i); i = sprintf(str, "%d", 15); printf("15 in decimal is %s\n", str); printf("sprintf returns: %d\n\n", i); i = sprintf(str, "%x", 15); printf("15 in hex is %s\n", str); printf("sprintf returns: %d\n\n", i); i = sprintf(str, "%f", 15.05); printf("15.05 as a string is %s\n", str); printf("sprintf returns: %d\n\n", i); return 0; }
Output:
15 in octal is 17 |
sscanf
For completeness, I'm going to cover sscanf, seeing that it's paired with sprintf.
You could've guessed that it converts a string into various formats.
sscanf takes three arguments, for example:
sscanf(str, "%d", &num);
The first is a char * variable that contains data to be converted.
The second is a string containing a format specifier that determines how the string is converted.
The third is a memory location to place the result of the conversion. Most of the time, you'll need the "address of" operator (&), then a variable name, or you can place a char * variable here.
Now, if the string you pass into sscanf contains a space, only the data up until that space is converted.
sscanf returns the number of items converted.
This example performs conversions in several formats:
#include <stdio.h> int main() { char* ints = "20, 40, 60"; char* floats = "10.4, 24.66"; char* hex = "FF, F"; int i; int n; float f; int h; char* s; i = sscanf(ints, "%d", &n); printf("n: %d\n", n); printf("sscanff returns: %d\n\n", i); i = sscanf(floats, "%f", &f); printf("f: %f\n", f); printf("sscanff returns: %d\n\n", i); i = sscanf(hex, "%x", &h); printf("h: %d\n", h); printf("sscanff returns: %d\n\n", i); i = sscanf(ints, "%s", s); printf("s: %s\n", s); printf("sscanff returns: %d\n\n", i); return 0; }
Output:
n: 20 |
Notice how sscanf ignores the comma when converting to a number (see the result for the string variable, s).
Prev: Copying, Finding the Length of
Strings and the Null Character
Next: Copying Strings:
strcpy, strncpy and strcmp
发表评论
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(转)const参数,const返回值与const函数
2014-11-14 17:29 822原文地址:http://04 ... -
(转)在 Eclipse 中配置编译 Pro*C
2010-08-09 17:49 2039http://blog.csdn.net/gjl2004yn/ ... -
(转)Pro*C 程序概述
2010-06-30 10:24 1147http://blog.csdn.net/amandake ... -
(转)什么是Pro*C/C++
2010-06-30 10:22 2321http://blog.csdn.net/hwz119/a ... -
(转)oracle中pro*c的学习
2010-06-30 10:17 1497http://www.qqread.com/ora ... -
(转)gcc and g++编译器和gdb调试器
2010-02-23 15:09 1871http://d.download.csdn.net/d ... -
(转)GDB 命令详细解释
2010-02-23 15:05 1533http://blog.csdn.net/wei801004/ ... -
CC和gcc是一样的编译器吗?
2009-06-15 17:06 2833楼主anysisze(张)2006-07-20 21:4 ... -
gcc常用参数,备忘
2009-06-12 14:45 1489gcc常用参数,备忘收藏 1. 头文件象conio ... -
请教关于标准C中findfirst()函数的用法!谢谢
2009-06-03 17:45 5058http://www.9php.com/FAQ/cx ... -
用strtok()函数提取分隔符隔开的每个字符串
2009-05-22 14:45 4178http://www.cplusplus.com/refere ... -
printf格式控制符的完整格式
2009-03-25 10:39 3210printf格式控制符的完整格式(2006-2-17 14: ... -
iconv 转码编程简介
2009-03-24 17:39 4413glibc带了一套转码函数 ... -
iconv 的使用方法
2009-03-24 17:38 1483iconv 的使用方法 iconv---编码转换用法: ic ... -
(C语言)头文件实现的函数
2009-03-18 17:43 4458(C语言)头文件实现的函数 http://www.diy ... -
C语言库函数大全(字母a)---使用说明(转)
2009-03-18 17:43 1626C语言库函数大全(字母 ... -
在 console mode 中使用 C/C++ 编译器
2009-03-05 17:18 1181在 console mode 中使用 C/C++ 编译器 ...
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